Fair Value of Assets and Liabilities (Changes in Level 3 Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	$ 4,166	$ 4,986	$ 4,153	$ 5,247
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	4,684	5,242	4,684	5,242
Total gains (losses) (realized/unrealized):
Included in earnings	518	256	531	(5)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	518	256	531	(5)
Equity Securities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Equity Securities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	518	256	531	(5)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	518	256	531	(5)
Equity Securities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Equity Securities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Short-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	12,349	0	10,000	0
Purchases	21,693	0	24,042	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(11,723)	0	(11,723)	0
Other	100	0	100	0
Transfers into Level 3	540	0	540	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	22,921	0	22,921	0
Total gains (losses) (realized/unrealized):
Included in earnings	(38)	0	(38)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(34)	0	(34)	0
Short-term investments | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(34)	0	(34)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(34)	0	(34)	0
Short-term investments | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Short-term investments | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Short-term investments | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	(4)	0	(4)	0
Cash equivalents
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	100	0	0	0
Purchases	38	0	138	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	(100)	0	(100)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	25	0	25	0
Total gains (losses) (realized/unrealized):
Included in earnings	(13)	0	(13)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(13)	0	(13)	0
Cash equivalents | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(13)	0	(13)	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(13)	0	(13)	0
Cash equivalents | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Cash equivalents | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Cash equivalents | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	63,072	12,242	53,980	8,059
Purchases	3,813	10,338	6,466	18,134
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(3,287)	(2)	(5,420)	(2)
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	68,305	27,136	68,305	27,136
Total gains (losses) (realized/unrealized):
Included in earnings	4,707	4,558	13,279	945
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,420	4,556	7,859	944
Other assets | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	4,707	4,558	13,279	945
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	1,420	4,556	7,859	944
Other assets | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Other assets | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Other assets | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Reinsurance recoverables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	271,390	565,090	409,013	302,814
Purchases	4,282	4,240	8,544	8,563
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	302,009	539,123	302,009	539,123
Total gains (losses) (realized/unrealized):
Included in earnings	26,337	(30,207)	(115,548)	227,746
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	28,643	(26,137)	(105,520)	232,325
Reinsurance recoverables | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	26,337	(30,207)	(115,548)	227,746
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	28,643	(26,137)	(105,520)	232,325
Reinsurance recoverables | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Reinsurance recoverables | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Reinsurance recoverables | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Future policy benefits
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(10,511,815)	(25,302,654)	(17,314,004)	(11,822,998)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(290,736)	(284,426)	(581,885)	(566,610)
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	(12,530,109)	(23,998,671)	(12,530,109)	(23,998,671)
Total gains (losses) (realized/unrealized):
Included in earnings	(1,727,558)	1,588,409	5,365,780	(11,609,063)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,837,883)	1,421,382	4,982,288	(11,807,482)
Future policy benefits | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(1,727,558)	1,588,409	5,365,780	(11,609,063)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(1,837,883)	1,421,382	4,982,288	(11,807,482)
Future policy benefits | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Future policy benefits | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Future policy benefits | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Policyholders' account balances
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	(986,479)	(158,920)	(580,184)	(196,892)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	(134,633)	(28,057)	(273,158)	(50,514)
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	(1,361,320)	(226,072)	(1,361,320)	(226,072)
Total gains (losses) (realized/unrealized):
Included in earnings	(240,208)	(39,095)	(507,978)	21,334
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(211,238)	(34,321)	(463,941)	10,084
Policyholders' account balances | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(240,208)	(39,095)	(507,978)	21,334
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(211,238)	(34,321)	(463,941)	10,084
Policyholders' account balances | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Policyholders' account balances | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Policyholders' account balances | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	(2,971)	(57)	(3,015)	(167)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(3,001)	(982)	(3,038)	(982)
Available-for-sale | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	4,556	8,799	3,569	(6,125)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	2,774	8,875	1,674	(7,191)
Available-for-sale | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	27	18	20	(3)
Available-for-sale | Fixed maturities | U.S. government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	15,000	11,458	15,000	10,547
Purchases	0	758	0	1,669
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	15,000	12,216	15,000	12,216
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Available-for-sale | Fixed maturities | Corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	165,910	111,606	148,687	104,267
Purchases	95,875	3,896	106,509	15,173
Sales	0	(7,810)	0	(8,965)
Issuances	0	0	0	0
Settlements	(23,695)	(3,445)	(31,322)	(5,810)
Other	0	0	0	0
Transfers into Level 3	0	10,783	15,147	25,132
Transfers out of Level 3	(8,235)	(244)	(8,235)	(244)
Fair Value, end of period	232,200	123,389	232,200	123,389
Total gains (losses) (realized/unrealized):
Included in earnings	2,345	8,603	1,414	(6,164)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	508	7,738	(523)	(8,042)
Available-for-sale | Fixed maturities | Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	16,956	24,227	18,542	18,825
Purchases	202,798	0	202,798	6,145
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(2,658)	(620)	(4,137)	(1,075)
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	(5,636)	0	(5,636)
Fair Value, end of period	216,363	18,128	216,363	18,128
Total gains (losses) (realized/unrealized):
Included in earnings	(733)	157	(840)	(131)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	(735)	155	(841)	(131)
Trading | Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, beginning of period	5,127	3,593	5,045	4,464
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Other	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair Value, end of period	5,350	4,301	5,350	4,301
Total gains (losses) (realized/unrealized):
Included in earnings	223	708	305	(163)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	224	713	311	(153)
Trading | Fixed maturities | Realized investment gains (losses), net
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Trading | Fixed maturities | Other income
Total gains (losses) (realized/unrealized):
Included in earnings	223	713	311	(153)
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	224	713	311	(153)
Trading | Fixed maturities | Included in other comprehensive income (loss)
Total gains (losses) (realized/unrealized):
Included in earnings	0	0	0	0
Unrealized gains (losses) for assets/liabilities still held:
Included in earnings	0	0	0	0
Trading | Fixed maturities | Net investment income
Total gains (losses) (realized/unrealized):
Included in earnings	$ 0	$ (5)	$ (6)	$ (10)